fix: blocks being dragged behind toolbox (#7619)

* fix: add layer manager to fix dragging

* chore: fix block animations

* chore: add tests

* chore: format

core/layers.ts

@@ -0,0 +1,19 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * The layer to place blocks on.
+ *
+ * @internal
+ */
+export const BLOCK = 50;
+
+/**
+ * The layer to place bubbles on.
+ *
+ * @internal
+ */
+export const BUBBLE = 100;